本教程使用 `FAISS` 向量数据库，该数据库利用了 Facebook AI Similarity Search（FAISS）库。

```bash
pip install faiss-cpu
```

我们想要使用 OpenAIEmbeddings，所以我们需要获取 OpenAI API 密钥。


```python
import os
import getpass

os.environ['OPENAI_API_KEY'] = getpass.getpass('OpenAI API Key:')
```


```python
from langchain.document_loaders import TextLoader
from langchain.embeddings.openai import OpenAIEmbeddings
from langchain.text_splitter import CharacterTextSplitter
from langchain.vectorstores import FAISS


raw_documents = TextLoader('../../../state_of_the_union.txt').load()
text_splitter = CharacterTextSplitter(chunk_size=1000, chunk_overlap=0)
documents = text_splitter.split_documents(raw_documents)

db = FAISS.from_documents(documents, OpenAIEmbeddings())
```

### Similarity search

```python
query = "What did the president say about Ketanji Brown Jackson"
docs = db.similarity_search(query)
print(docs[0].page_content)
```

<CodeOutputBlock lang="python">

```
    Tonight. I call on the Senate to: Pass the Freedom to Vote Act. Pass the John Lewis Voting Rights Act. And while you’re at it, pass the Disclose Act so Americans can know who is funding our elections.

    Tonight, I’d like to honor someone who has dedicated his life to serve this country: Justice Stephen Breyer—an Army veteran, Constitutional scholar, and retiring Justice of the United States Supreme Court. Justice Breyer, thank you for your service.

    One of the most serious constitutional responsibilities a President has is nominating someone to serve on the United States Supreme Court.

    And I did that 4 days ago, when I nominated Circuit Court of Appeals Judge Ketanji Brown Jackson. One of our nation’s top legal minds, who will continue Justice Breyer’s legacy of excellence.
```

</CodeOutputBlock>

### 通过向量进行相似性搜索 (Similarity search by vector)

还可以使用 `similarity_search_by_vector` 来搜索与给定嵌入向量相似的文档，该函数接受一个嵌入向量作为参数，而不是一个字符串。

```python
embedding_vector = embeddings.embed_query(query)
docs = db.similarity_search_by_vector(embedding_vector)
```
